The curtain wall is a building exterior wall fabricated using a number of panels 11 installed side by side as shown in FIG. 8. The installation of the panel 11 is currently made with a vertical frame 13 and a horizontal frame 14. They are locked in place with mounting brackets 15 on vertical sub-frames 12, installed at the edge of a floor portion 5 of the building. The panel 11 is fixed to the frames 13 and 14.
Curtain wall panels are usually made of an aluminum alloy plate 4.5 mm to 6 mm in thickness and installed with formed aluminum frames for reinforcement to give sufficient stiffness. This structure, however, results in design difficulties in the production of large sized panels because uniformity of the panel reinforcement cannot be ensured, and this inevitability results in the use of many panels 11. This also results in an unsatisfactorily close arrangement of the vertical sub-frames 12 and dense arrangement of frames 13 and 14. Existing walls are also subject to distortion through alternate heating by the sun and cooling. Therefore, existing tall building construction requires large quantities of installation materials and processes and frequent delivery of materials. This problem has forced the construction industry to look for a new type of curtain wall using large sized panels.
To solve the above described problems that occur in the use of aluminum alloy plate for paneling, a curtain wall structure using honeycomb panels has been proposed. The honeycomb panel is made with an outer plate of approx. 1.5 mm in thickness and an inner plate approximately 1.0 mm in thickness bonded together, and has an overall thickness of between 15 and 40 mm resulting in greater rigidity and surface flatness as compared with current types made of aluminum alloy plate. This new type of honeycomb panel has the advantage of a high degree of flatness: an essential factor for good external appearance of building panels.
Conventional technical and economical factors do not permit production of panels thicker than the above described examples because of poor production yields of honeycomb core. This limitation requires additional bracing frames to be installed behind the panel to carry its weight and external forces applied on the curtain wall caused by wind pressure and the sun-heating cycle. Additional frames, therefore, are needed on the back of the honeycomb panels. The frames are mounted on the building main frame using mounting brackets. The frames also play the role of joining together and sealing adjacent frames, water sealing and joining to glass panels. External pressures such as wind pressure exerted on the honeycomb panel are transferred to the building main frame through the frames.
As a total structure, honeycomb panels are used only as panels of good flatness and stiffness, being attached to supporting frames. This means that the use of conventional honeycomb panels also requires installation of supporting unit frames, diagonal braces and transoms. These additional members are manufactured separately and assembled on the reverse side of each panel. The frames, therefore, are not stiffness-providing supports of the honeycomb panels but simply part of the assembly, and the warping stiffness becomes a simple sum of the stiffness of each section. This limits the maximum size of larger panels because of comparatively low stiffness per unit weight, besides the additional problem that the total thickness of the panels and the supporting frames becomes inconveniently large. A further problem is that the total thickness of the panel plus its supporting members increases.
Furthermore, the water sealant where the panels are joined together can be no thicker than the honeycomb panels themselves. When thin panels are used, the sealing is done on site using a caulking rubber sealer. This may result in breakage of the seam line caused by thermal expansion and shrinkage if the panel size is large. This phenomenon also limits the size of panels made of thin honeycomb panel.